204
FXUS66 KLOX 201836
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1136 AM PDT Fri Sep 20 2024

.SYNOPSIS...20/946 AM.

Shower and thunderstorm chances have shifted to LA County and
eastern Ventura County today as a cold upper continues to move
through the area. Some showers or thunderstorms could have heavy
downpours, and gusty winds. High pressure will build in over the
weekend and bring a significant warming and drying trend to the
region over the weekend into early next week.

&&

.SHORT TERM (TDY-SUN)...20/1004 AM.

***UPDATE***

The upper low has moved southeast and is currently between Palos
Verdes and Catalina. A line of showers and thunderstorm stretches
from Mojave to eastern Ventura County, though most of the storms
are north of Antelope Valley. A the day goes along and the low
continues to shift to the southeast, that line will pivot to a
north/south orientation and focus on the eastern portion of LA
County, including the Bridge fire area. Showers and thunderstorms
chances will continue in that area through early evening with
periods of heavy rain possible. Steering flow is expected to be
15-20 kt from the north, but some training of storms is possible.
Moisture profiles today are not as favorable for significant
flooding today but can`t rule it out entirely. Latest hi res
ensembles show the 90th percentile for hourly rain rates peaks at
around .60 inches, which is about a quarter inch shy of the
thresholds for burn area debris flows, so for now will not be
issuing a flash flood watch.

Precip expected to taper off this evening with dry and warmer weather
over the weekend.

***From Previous Discussion***

A mostly north to south flow on the back side of the low pressure
trough will steer any shower activity from the mountains into the
valleys and coastal areas later today and into this evening. The
trough`s slower movement has contributed to PoPs being held on for
longer the system has slowed down. The highest PoPs are indicated
over the mountains and into the foothills of the mountains, but
showers and thunderstorms pushing into Southland valley area and
into the Ventura County coastal plain seems elevated in
confidence at this point.

Otherwise, a cooler air mass will continue across the area
through tonight as a deep marine layer depth will remain in place.
Clouds are pushing well into the coastal slopes of the mountains
this morning, even with the disturbed and weaken marine inversion
over the region at this time.

A marginally tight northerly surface gradient could bring some
sub-advisory northwest to north winds across southern Santa
Barbara County mountains this evening and through the Interstate 5
Corridor tonight. Gusts to between 30 and 40 mph will likely be
observed with local gusts up to 45 mph in a few spots.

A drying and warming trend will take place over the weekend as the
upper-level trough will move off to the east. High pressure aloft
will nose into the region and bring much temperatures, especially
Sunday and Monday. Night through morning low clouds and fog should
remain in the forecast for tonight, then much less marine coverage

.LONG TERM (MON-THU)...20/357 AM.

The latest forecast ensembles agree that Monday will likely be
the warmest day of the week. Low cloud coverage could end up being
confined to the coast by Monday morning as onshore flow weakens.
There is still a large spread of solutions for the remainder of
next week, the forecast ensembles lean trend toward a cooling
trend for Tuesday and Wednesday. The forecast temperatures break
away from NBM values for Monday, but otherwise, keeps the NBM
values for now. Forecast ensemble leans towards a cooler air mass
with more marine influence for Tuesday, Wednesday, and Thursday.

&&

.AVIATION...20/1835Z.

At around 17Z at KLAX, there was a deep moist layer up to roughly
4500 feet. The top of the weak inversion was at 6000 feet with a
temp of 12 C.

Moderate confidence in TAFs for KPMD and KWJF. There is a 20-30%
chc of TSTMs thru 06Z.

Low confidence in LA county TAFs. There is a 10-20% chance of
TSTMS for KBUR AND KVNY thru 00Z. At KLAX, KSMO, and KLGB, there
is a <10% chance of TSTMs this afternoon thru 00Z and a 10-20%
chance of -DZ.

Low confidence in remaining TAFs due to the uncertainty of cigs
arrival time and height. There is a 20% chance KPRB remains VFR
thru the period. There is a chance for VLIFR conds at KSMX (40%)
and KSBP (30%) between 03Z and 16Z.

For all coastal and valley sites, arrival of cigs may be off by
+/- 5 hours from current forecast. The flight cat may be off by at
least one cat during any point once cigs arrive.

Any thunderstorms that form may produce brief +RA and gusty,
erratic winds.

KLAX...Low confidence in TAF. There is a <10% chance of TSTMs
this afternoon thru 00Z and a 10-20% chance of -DZ. There is a
30% chance BKN010-020 may arrive as early as 02Z. There is a 10%
chance for cigs BKN008-010 between 02Z-15Z, or once cigs arrive.
There is a 30% chance for VFR conds by 18Z-20Z Sat. No
significant east wind component expected.

KBUR...Low confidence in TAF. There is a 10-20% chance of TSTMs
thru 00Z. Low confidence in hgt and timing of CIGs, which might be
off +/- 3 hours from current forceast and be between BKN008-015.

&&

.MARINE...20/838 AM.

Isolated thunderstorms will be possible across the eastern
portion of the Santa Barbara Channel through the southern inner
waters and out to Santa Cruz Island into the afternoon. Any
thunderstorm that forms has the potential for frequent cloud to
surface lightning, gusty and erratic winds with rough seas, and
small hail.

For the Outer Waters (Central coast south to San Nicolas
Islands), moderate to high confidence in the forecast. High
confidence in winds and seas remaining below Small Craft Advisory
(SCA) level thru early next week in the northern zone (off the
Central Coast) except for a 20-30% chance of SCA level winds this
afternoon thru evening. For the southern zones (Pt Sal to San
Nicolas Island), there is a 60-70% chance of SCA level winds
through late tonight across the waters from Point Conception to
San Nicolas Island, with the furthest southern zone already
hitting SCA levels this morning. From Saturday thru Wednesday,
high confidence in winds and seas remaining below SCA level, and
then there is a 20-30% chance of winds picking up Wednesday night.

For the inner waters along the Central coast, high confidence in
conds remaining below advisory levels through Wednesday.

For the Santa Barbara Channel, moderate confidence in the
forecast. There is a 50-70% chance of SCA level wind gusts across
the western portion of the channel this afternoon through evening
with a 20% chance of winds extending into the eastern portion,
therefore a SCA was issued. Then, moderate to high confidence in
conditions remaining below SCA levels through Wednesday.

For the inner waters off the coast of LA and Orange Counties,
moderate to high confidence in conditions remaining below
advisory levels through Wednesday. However, there is a 20-30%
chance of SCA level wind gusts thru the San Pedro Channel Sun
afternoon.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Saturday for zones 650-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Saturday for
      zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Hall
AVIATION...Lewis
MARINE...Lewis/Lund
SYNOPSIS...MW

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox